The prior art teaches many systems for the delivery of pharmaceutically beneficial agents. One such system operates by means of an osmotic pumping mechanism. However, it suffers from being very complex and is complicated to manufacture. A second type of pharmaceutical delivery system utilizes hydrogels either from a group consisting of uncrosslinked linear polymers or from a group consisting of crosslinked polymers. In devices using uncrosslinked polymers, viscosity is the rate controlling factor for drug release kinetics. In these systems a gelatinous layer is formed on the surface upon hydration. The thickness and durability of this gelatinous layer depends upon the concentration, as well as the molecular weight and viscosity of the polymer in the device. At higher concentrations the linear polymer chains entangle to a greater degree leading to virtual crosslinking and a stronger gel layer. Drug release is by the dissolution of polymer and erosion of the gel layer and hence the rate of erosion is what controls the release rate. Although viscosity is an important consideration in controlled drug release from hydrogel matrices, it is viscosity under low shear conditions that control diffusion through the matrix.
Several U.S. Patents are directed to the various pharmaceutical delivery systems as mentioned above, see for example U.S. Pat. Nos. 3,845,770, 3,916,899, 4,016,880, 4,160,452 and 4,200,098. While these systems do provide for the delivery of a selected pharmaceutical agent, none of these provide a controlled or pulsatile delivery of the pharmaceutical agent in which drug release is modulated by combining a microbial polysaccharide and uncrosslinked polymer. Furthermore, none of the prior art teaches a device comprising a microbial polysaccharide and uncrosslinked polymer and optionally a crosslinked polymer and/or lipophillic polymer and/or saturated polyglycolyzed glyceride.
There was therefore a need to develop a novel controlled release pharmaceutical delivery device which could be made in a cost efficient manner and provide for either sustained or pulsatile delivery of the selected pharmaceutical incorporated therein.